Russian Ambassador to Ankara Andrey Karlov announced during an interview that his country does not consider the outlawed Kurdistan Workers’ Party (PKK) to be a terrorist organization, a statement that will likely further exacerbate rising tensions between Turkey and Russia.

“We understand Turkey’s concerns with regard to global terrorism. Especially after the terrorist attack in Ankara the other day. But neither the Kurdistan Workers’ Party (PKK) nor the Democratic Union Party (PYD) are considered terrorist organizations by either Russia or the United Nations Security Council,” said Russian Ambassador to Ankara Andrey Karlov during an interview with Russian news agency Ria Novosti.

He added that while Russia had contacted Syrian Kurdish representatives, they did not have any contacts within the PKK.

The comments come at a time of escalating tension between Ankara and Moscow, after Russia initiated an air campaign in support of Syrian President Bashar al-Assad three weeks ago.

Having lobbied for Assad’s removal for years, Turkish President Recep Tayyip Erdoğan has harshly criticized the operations, as well as the repeated airspace violations by Russian jets since airstrikes began.

Turkey also suspects Russia of lending support to the Syrian Kurdish PYD and its armed wing, the People’s Protection Units (YPG), since the air strikes began three weeks ago.

Turkey considers the PYD a terrorist organization, having links to the PKK. Ankara fears that any territorial gains by Kurds in Syria – let alone the establishment of an independent state – might incite similar ambitions from its own Kurdish minority.

“No one can guarantee that arms given to the PYD today won’t fall into the hands of the PKK tomorrow and be used against Turkey,” acting Prime Minister Ahmet Davutoğlu said on Wednesday. “Turkey cannot accept any kind of cooperation with terrorist organizations that have declared war against Turkey.”

However, during his interview with Ria Novosti, Ambassador Karlov explicitly denied that Russia had delivered any arms to Syrian Kurds.

Emerging as a reliable force in the fight against the Islamic State of Iraq and the Levant (ISIL), the PYD has also garnered the support of the United States, with U.S. officials stating that the PYD is not considered a terrorist organization under U.S. law.

Both Russian Ambassador Karlov and U.S. Ambassador John Bass were summoned to the Ministry of Foreign Affairs in Ankara earlier this week to hear Turkish concerns over their cooperation with Kurdish forces in Syria.